Nextsmaller.java

import java.util.*;
public class Nextsmaller {
    public static void nextSmaller(int arr[], int arr1[]){
        Stack <Integer> s = new Stack<>();
        for(int i = arr.length-1; i>=0; i--){
            //while loop
            while(!s.isEmpty() && arr[s.peek()] >= arr[i]){
                s.pop();
            }
            if(s.isEmpty()){
                arr1[i] = -1;
            }
            else{
                arr1[i] = arr[s.peek()];
            }
            s.push(i);
        }
    }
    public static void main(String args[]){
        int arr[] = {1,2,3,4,3};
        int nSmaller[] = new int[arr.length];
        nextSmaller(arr, nSmaller);

        for(int i = 0;i<nSmaller.length; i++){
            System.out.print(nSmaller[i] + " ");
        }
    }
}